Braun tube



April 4, 1939. K. SCHLESINGER BRAUN TUBE Filed Sept. 28, 1954 I.7huenlor Patented Apr. 4, 1939 UNETED STATES PATENT QFFEQE BRAUN TUBESteglitz, Germany Application September 28, 1934, Serial No. 745,952

In Germany 3 Claims.

The invention relates to a Braun tube, more particularly for televisionpurposes, in which merely comparatively low potentials are required fordeflection of the ray, and means are provided 5 in order to make theform and size of the image point constant and independent of itsintensity and of its position on the image screen.

t has already been proposed in one of. the earlier applications of theapplicant to concentrate the controlled electronic ray proceeding fromthe cathode on to a diaphragm, and to reproduce this diaphragm on theimage screen by means of a suitable electron-optical system. In thisarrangement the deflecting system is situated between theelectron-optical system and the fluorescent screen.

It has also already been proposed to employ a so-called electron-gun,and to obtain the concentration by means of a field, which is producedby means of a metallic coating on the bulb of the tube linked up withhigh potential.

In this arrangement the concentration is effected by field lines fillingthe entire space between the fluorescent screen and the electron gun.

The deflecting systems in this arrangement are situated within theconcentration field itself, so that the distribution of the field in thevicinity of the first deflecting system is different 30 from that in thevicinity of the second deflecting system. In consequence it isimpossible with these arrangements to operate with electrostaticdeflecting systems.

These known arrangements do not permit of the production of televisionimages, which possess an even structure over their entire surface.

The object of the invention is a Braun tube which allows of theproduction of completely regular images.

According to the invention:

1. The controlled electronic ray is preliminarily concentrated onto a.diaphragm,

2. The diaphragm is reproduced on the image screen by means of anelectron-optical system, which acts preferably as a relatively thincollecting lens (of, for example, 3 cm. in thickness),

3. The deflection necessary for producing the line screen is performerprior to entry of the cathode ray into the lens, preferably in acompletely fleldless space,

4. The deflection is preferably performed by a system, which causes bothdeflections in the same plane, for example according to the patentapplication Ser. No. 726,477, filed May 19, 1934.

October 2, 1933 5. A substantially fleldless space is provided betweenthe electron-optical system and the fluorescent screen.

The simultaneous use of all of the stated measures is particularlyconvenient; the single measures, however, are also of particularimportance per se, and may also be employed singly or in partialcombination.

A form of embodiment of the tube according to the invention isillustrated by Way of example in the drawing, in which Fig. 1 shows apossible total arrangement of the tube, while in Fig. 2 there is shown aparticular form of embodiment of. the preliminary concentration system,and in Fig. 3 a form of embodiment of the deflecting system.

Figs. 4 and 5 show particular forms of embodiment of the lens accordingto the invention.

In Fig. l:

I is the bulb of the tube, which consists of the neck portion 2 and thepreferably spherical envelope portion 3. The fluorescent screen 4 mayeither be suspended in the bulb, or constructed inside the form of afluorescent layer 5 applied in direct fashion to the wall of the bulb.The electrons proceeding from the cathode 6, which conveniently isconstructed in the form of an indirectly heated large surface cathodehaving an emissive layer sunk into the surface, are preliminarilyconcentrated on to the diaphragm. II] by means of a system consisting,for example, of, the cylinder 1 and the preliminary anode 8 and anadditional cylinder 9. In this connection the cylinder 1 may possess aweakly negative bias, the preliminary anode 8 and the diaphragm l0 maybe raised to a weak positive potential (for example +300 Volts), and thepotential of the cylinder 9 be weakly negative (for example +200 volts)in relation to the diaphragm 8.

The control takes place by applying the control alternating potential tothe control plate ll arranged in the cylinder 1 preferably at a distancefrom the cathode 6 corresponding to the cathodic dark space with usualgas pressures and preferably in conductive connection with the cylinder.Preferably the system. may be adjusted in such fashion that theelectronic ray at its maximum intensity passes through the preferablysmall aperture l2 (for example 1 mm?) of the diaphragm [0 Without beingpartly stopped by said diaphragm l2 (for example 1 mm?) of the diaphragmIll.

The diaphragm aperture I2 is reproduced on the fluorescent screen bymeans of the electronoptical system comprising the perforated plate I3and the annular collar I4. The spacing between the diaphragm to bereproduced and the lens (object spacing) on the one hand and between thelens and the fluorescent screen on the other hand may preferably be soselected (for example in the ratio of 2:1) that the diaphragm isreproduced on the image screen on reduced scale (for example 1:2). Forexample, the objeot spacing may be selected at 300 and the image spacingat 150 mm.

The annular plate I3, which is connected with a low positivepotential-preferably the same potential as the diaphragm Ill-has at thesame time the object of screening off the alternating field of thedeflecting plates against the lens.

The deflecting system I1, I8, the aperture of which directed towards theplate I3 is preferablyeither by inclined or by parabolic construction ofthe deflecting elements-made larger than the inlet aperture, mayconveniently be disposed as close as possible to the plate I3, forexample at a distance of very few millimeters from the same.

As already set forth, the deflecting system is situated in the entirelyfieldless space between the electrodes I!) and I3. The space betweenthese electrodes may be screened off towards the outside by means of ametallic tube connecting the electrodes or also by a metallic coating onthe neck of the tube having a corresponding length and being raised tothe same potential as the electrodes I and I3.

The second electrode of the electron-optical system, the annular plateI4, is preferably constructed, according to the invention, as a narrowor very narrow ring fitting closely against the wall of the bulb. A partof the wall of the bulb between this electrode and the fluorescentscreen is furnished with a metallic coating, which is conductivelyconnected with the electrode I4, and in consequence possesses the samepotential as this electrode (for example 2000 volts).

Since the wall of the bulb greatly recedes immediately behind theelectrode, the relatively weak field formed between the electrode I4 andthe fluorescent screen does not appreciably participate in the opticaleffect of the system.

The metallic coating of the bulb in substance produces the effect thatthe wall charges are neutralised and deformations in the shape of theimage caused by the same avoided.

Instead of connecting the metallic coating I5 with the electrode I4 itis sometimes convenient to impart to the same a potential which isweakly negative (for example to the extent of 100-300 volts) in relationto the electrode I4.

In place of the preliminary concentration system illustrated in Fig. 1,it is also possible, for example, to employ this system shown in Fig.2.In the figure:

6 is the cathode, I the cylinder constructed as described in Fig. 1 withthe control plate I I, 8 a preliminary anode, and I 0 the diaphragm withthe aperture I2. The system is adjusted in such fashion by suitableselection of the potentials that the cathode ray in the case of itsmaximum intensity passes through the aperture I2 without being partlystopped by the diaphragm I0.

In this form of embodiment it is particularly important to selectcorrectly the sizes and also the spacing of the different elements.

If the Wehnelt cylinder 1 is to be operated with a very weak negativebias (for example in the light condition: zero) and a weak positivepotential of, for example, +300 volts is applied to the preliminaryanode 8, the diameter of the cylinder I maybe selected at mm., thedistance of the plate I I from the cylinder edge (the extent ofintroduction) at 1.5 mm., and the distance of the cylinder 1 from theplate 8 at 2 mm.

In the Braun tubes hitherto known the deflecting systems are arranged inaxial consecution, at a relatively large distance apart.

It is absolutely essential in the case of these arrangements to disposethe systems at a comparatively large distance apart, as otherwise amutual interference effect of the deflecting fields takes place, whicheffect results in distortion and curvature of the image.

This known arrangement of the deflecting systems in axial consecution,however, results in the fact that the spacing of the pivot point of theray in the two deflecting directions from the lens is of differentamount, so that the conditions under which the ray passes the lens arenot the same in respect of the two directions of deflection, and thatfurther the lens requires to possess a very large aperture.

According, therefore, to the invention, there is conveniently employedfor deflecting purposes a system according to the patent applicationSer. No. 726,477, filed May 19, 1934 which enables the defiection to beperformed in both directions in the same plane without any mutualinterference of the deflecting fields.

According to the invention, the line frequency deflection takes place bythe use of an electrostatic field, whilst for frame frequency deflectionpurposes there is employed an electro-magnetic field. The elementsacting as static deflecting plates are then conveniently constructedthemselves as pole shoes for the magnets causing the frame frequencydeflection. These plates, in accordance with the invention, may alsoconveniently be tilted in relation to each other, or constructed incurved form.

A form of embodiment of the deflecting system according to the inventionis illustrated by way of example in Fig. 3.

In the same:

2 is the neck of the tube, and I1 and I8 are the deflecting elements,which are supplied which on the one hand, in the manner known per se,with the potentials necessary for electrostatic deflection, and which atthe same time are constructed as pole shoes for the magnets I9 and 20causing the frame frequency deflection. The elements I! and I8 arepreferably constructed in such fashion that the same extend as closelyas possible towards the Wall of the tube. The tube I 6 connecting thediaphragms I0 and I3 (cf. Fig. 1) may in this case conveniently befurnished with recesses, through which the elements II and I8 project.

Various forms of embodiment of an electron lens may be employed in placeof that set forth in Fig. 1. Thus, for example, it is possible tofurnish the glass bulb I at that particular point at which the lens isto be mounted with two metallic annular coatings insulated one againstthe other, of which coatings the one is connected with a weak and theother with a strong positive potential.

The refractive power of the lens is determined in this case inter aliaby the spacing between the two annular coatings, and may be adjusted asdesired by variation of this spacing.

It is also convenient in the case of this embodi ment to screen ofi" thedeflecting systems against the lens field by means of a diaphragm, whichconveniently may be connected with the potential of the weakly positivecoating.

A form of embodiment of a lens of this nature is illustrated by way ofexample in Fig. 4. In the same:

I is the glass envelope, I1 and I8 are the deflecting elements, and I3is the screening diaphragm. On the glass Wall itself there are providedthe two coatings 2i and !5. The coating 2| is supplied with a weakpositive potential (for example 300 volts) and the coating 15 with theanode potential (for example 2000 volts).

In order to prevent the ray from being appreciably further influenced inthe space between the electron lens and the fluorescent screen there isconveniently provided a diaphragm l4, which may consist of a narrowannular collar, and preferably be conductively connected with themetallic coating Hi. The diaphragm M, in ac cordance with the invention,may also be replaced by a small metallic tube 22, which extends for ashort distance, for example mm.-3 cm. into the interior of the bulb(Fig. 5).

It is also possible to emply in lieu of the forms of lens as describedelectron-optical systems of other types.

It is convenient according to the invention, particularly at thosepoints at which there is situated the inner coating connected with a lowpositive potential, to furnish at the same time the outside with ametallic coating, and to connect this outer coating with earth.

According to a further feature of the invention two pairs of deflectingplates arranged in axial consecution in the described field-free spacemay be used. For this purpose each of the systems is arranged strictlysymmetrically with respect to the electronic lenses and to the tube axisand one plate of each pair is supplied with the respective deflectingvoltage, While the other plate is supplied with a voltage of the sameamplitude but reverse phase.

The necessary voltage of reverse phase may be easily produced with theuse of a phase reverse valve controlled by the output voltage of one ofthe well known relaxation oscillation generators, said valve having apotentiometer arranged in its output circuit, the desired reverse phasevoltage being tapped at said potentiometer so as to have the samepotential as the original deflecting voltage.

Deflecting systems of this kind have been found to have no disturbingeffect neither upon each other nor upon the field of the electric lens.

I claim:

1. A Braun tube for television purposes comprising an evacuated envelopeenclosing a cathode, a modulating grid mounted in the vicinity of saidcathode, a plate having an aperture, said plate being mounted in thevicinity of said grid, a picture receiving screen, an electrostaticalelectron-optical system mounted between said plate and said screen forreproducing said aperture on said screen, one pair of deflecting coilsfor deflecting the cathode ray in one direction, and one pair ofdeflecting plates for deflecting the cathode ray in a directionperpendicular to the first said one, said deflecting plates and saiddeflecting coils being mounted along the same axis, said deflectingplates being mounted between said plate. and said electron-opticalsystem in close proximity to said system, the distance between saidelectron-optical system and said plate having said aperture being atleast as great as the distance between said system and said screen.

2. A Braun tube for television purposes comprising an evacuated envelopeenclosing a cathode, a modulating grid mounted in the vicinity of saidcathode, a plate having an aperture, said plate being mounted in thevicinity of said grid, a picture receiving screen, an electrostaticalelectron-optical system mounted between said plate and said screen forreproducing said aperture on said screen, said electron-optical systemcomprising two electrodes, each of said electrodes comprising a cylinderhaving an apertured plate mounted therein and having an open cylindricalportion protruding beyond this apertured plate in the direction towardsthe other one of said electrodes, the two cylinders being adapted tohave different constant potentials impressed thereon, and deflectingmeans for deflecting the cathode ray in two directions perpendicular toeach other.

3. A Braun tube for television purposes comprising an evacuated envelopeenclosing a cathode, a modulating grid mounted in the vicinity of saidcathode, a plate having an aperture, said plate being mounted in thevicinity of said grid, a picture receiving screen, an electrostaticalelectron-optical system mounted between said plate and said screen forreproducing said aperture on said screen, said electron-optical systemcomprising two electrodes, each of said electrodes comprising a cylinderhaving an apertured plate mounted therein, the diameters of saidcylinders being equal, the diameters of the apertures of the platesinserted in said cylinders being different from one another, said twocylinders being coaxially arranged and being adapted to have difierentpotentials impressed thereon, and deflecting means for deflecting thecathode ray in two directions perpendicular to each other for scanningsaid picture receiving screen.

KURT SCHLESINGER.

